The present invention is directed to a reference electrode assembly and a process for construction therefor and specifically a reference electrode useful for operation in aqueous solutions at supercritical temperatures.
In power generating systems such as fossil power plants, the high temperature water used at supercritical temperatures (at or above 374.degree. C.) becomes very corrosive towards metals. To monitor corrosion, two important parameters necessary are electrochemical corrosion potential (ECP) and pH. It is desirable to continually monitor these parameters. However, long term monitoring in fossil plants is only possible by using corrosion reference electrodes and pH sensors that have proved ability to withstand supercritical temperatures over a long period of time. In the past, research has been performed to develop techniques for measuring potential and pH in high temperature aqueous systems. For lower temperature nuclear systems(e.g., 284.degree. C.), a solid polymer electrolyte based Ag/AgCl reference electrode was used in which the solid polymer electrolyte contained a chloride ion. Such an electrode is described in the Journal of Electrochemical Society, Vol. 134, page 1307 (1987), co-authored by S. Hettiarachchi and D. D. Macdonald inventors of the present application) and titled "A Solid Polymer Electrolyte Internal Reference Electrode For High Temperature Aqueous Systems." However, Teflon (a trademark) is used in the construction of this electrode. At temperatures above 320.degree. C., reference electrodes free of Teflon are required. In summary, the existing technologies have had two fundamental limitations; the first is the material stability and the second is lack of integrity as the temperature and pressure cycles between expected extremes.